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amplifier design - Av=10000, swing=1.8v, Vdd=1.8

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laperla

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Hi
I want to design amplifier with
Av=10000 &
swing=1.8v
Vdd=1.8

what kind of amplifier can i use for design?
 

Re: design amplifier

You will never be able to really reach 1.8V swing at the output, but you can get quite close. A standard 2-stage opamp should do the trick..
 

    L

    laperla

    Points: 2
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Re: design amplifier

thanks a lot solidstate
Can I use other amplifiers for these results?
 

design amplifier

Well, you need to have a rail-to-rail output stage, and some gain before it to reach 10k, which is your DC gain, I suppose. Maybe you could give some more info on where this amp is going to be used, and some more specifications? (bandwidth for example)

There is a lot of info on opamps on the internet, google is your friend as well ;)
 

Re: design amplifier

Tnx a lot
wide BW and Power<10m Routmax
 

Re: design amplifier

I think you will need a more complex design than a simple 2 stage to get rail to rail output. It also depends on if you want rail-rail input. There are plenty of ideas for opamp stages in text books. Also, look at the JSSC 1998 Volume 33 No. 10 Page 1482.

Keith.
 

design amplifier

Why do you think that? You can get all your gain in the first stage, and the second stage can be rail-to-rail..
 

Re: design amplifier

solidstate said:
Why do you think that? You can get all your gain in the first stage, and the second stage can be rail-to-rail..
Click to expand...

True. I just looked at some of my old designs and they are only 2 stage - they just look bigger than that because of the folded cascode mirrors, and complex output stage biasing. My mistake.

Keith.
 

design amplifier

are you designing it on simulation....

or you need real practical amplifier... if you it is not at all possible....

you cant get swing and vdd same... you can get this only if you have vss not grounded but some negative value if -1.8v than best...
 

Re: design amplifier

keith1200rs said:
solidstate said:
Why do you think that? You can get all your gain in the first stage, and the second stage can be rail-to-rail..
Click to expand...

True. I just looked at some of my old designs and they are only 2 stage - they just look bigger than that because of the folded cascode mirrors, and complex output stage biasing. My mistake.

Keith.
Click to expand...

Mind you, at 1.8V you might struggle with 60dB open loop gain, depending on the design and the process.

Keith.
 

design amplifier

You do have a point; one could argue that a cascode is also a stage.. Let's just roughly say that to get 10K gain if the gmRo of a device is in the order of 30, you need at least 3 of them!
 

Re: design amplifier

Hi
I have broblem with swing.with rail to rail, in the best situation swin=1.6
I can't give 1.8v
Could you give me schematic of rail to rail?
tnx
 

Re: design amplifier

laperla said:
Hi
I have broblem with swing.with rail to rail, in the best situation swin=1.6
I can't give 1.8v
Could you give me schematic of rail to rail?
tnx
Click to expand...

Have a look at the JSSC 1998 Volume 33 No. 10 Page 1482. You will find rail-rail output stages in many IC design text books.

Keith.
 

design amplifier

1.6V is pretty much as good as it gets (closed loop, if you still want gain). If your amplifier outputs exactly 0 or vdd, it has clipped (like an inverter).

Keith, nice read, I know these guys quite well btw ;)
 

Re: design amplifier

tnx
Could you give me link of this paper?
 

Re: design amplifier

solidstate said:
1.6V is pretty much as good as it gets (closed loop, if you still want gain). If your amplifier outputs exactly 0 or vdd, it has clipped (like an inverter).

Keith, nice read, I know these guys quite well btw ;)
Click to expand...

It's a nice amplifier design. The JSSC is a great source of ideas, I find. I am often stunned by some of the work people do!

Keith.

Added after 5 minutes:

laperla said:
tnx
Could you give me link of this paper?
Click to expand...

If you are an IEEE member you should be able to download it. If you are a student, I would expect your college/university will have access to back issues of the JSSC. It is probably copyrighted so I cannot post it.

Keith.
 

Re: design amplifier

In this paper all condition for Vsup>2.5
In my project Vdd=1.8
Is Vsup equal with Vdd?
 

Re: design amplifier

Hello all,

If you want to get a rail to rail output and only used a two stage design, and still get 10K...80dB. That will be hard. I could see it being possible if you used a folded cascode with gain boosting amplifiers. But you would have to do boosting. A folded cascode is usually good for 40 to 50dB. It also depends on the process. and min L used.

John
 

Re: design amplifier

tnx john
the problem of cascode is swing. swing=Vdd-4Vod
technology is TSMC 0.18um
 

design amplifier

You can cascode in .18um but the trick is using a native nmos for the bottom mirror then a wide swing for the pmos side. Just make sure your overdrives aren't to large. whats your Vth?

If you truely can't cascode.. but I think you can since i cascode in 90nm then make a three stage design. You can get 80dB easy with class AB output

John
 

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